Copernican System

Copernican System, systematic explanation of the movement of the planets around the Sun; a heliocentric (Sun-centered) system proposed in 1543 by the Polish astronomer Nicolaus Copernicus in the book De Revolutionibus Orbium Coelestium (On the Revolutions of the Celestial Spheres). The Copernican system advanced the theories that Earth and the planets are all revolving in orbits around the Sun, and that Earth is spinning on its north-south axis from west to east at the rate of one rotation per day. These two hypotheses superseded the Ptolemaic system, which had been the basis of astronomical theory since the second century ad, based on earlier ideas of Aristotle and others. According to the Ptolemaic system, Earth was the unmoving center of the universe and the Sun, Moon, planets, and stars all circled Earth.

The Copernican system also described the gradual shift of the Sun’s position through the constellations at spring equinox, a phenomenon called precession of the equinoxes.

The Italian astronomer Galileo became a strong advocate of Copernicus’s ideas, bringing him into conflict with the Catholic Church, which officially banned Copernicus’s book until the 19th century. Publication of the Copernican system stimulated the study of astronomy and mathematics, and laid the basis for the discoveries of the German astronomer Johannes Kepler and the British physicist and astronomer Sir Isaac Newton. See History of Astronomy.